Electrical energy supplied to airborne equipment includes two types, i.e., alternating current (AC) and direct current (DC). Generally, AC power supply for airborne equipment is implemented by designing a secondary power system.
Secondary power systems for different airborne equipment differ greatly in design. FIG. 1 is a block diagram of a secondary power system for airborne equipment, and in the secondary power system, a primary power source that can provide 28V DC power is used to supply power for the secondary power system. The main circuit includes a fuse 5, a filter 6, a convertor 7 and the like. The function of the fuse 5 is providing safety protection, when an input current increases rapidly due to an abnormal condition such as over-voltage of the primary power supply, a short circuit occurring in a latter-stage load circuit, or the like, the fuse 5 is disconnected to ensure the safety of the primary power circuit as well as the convertor 7 and the latter-stage load circuit. The filter 6 is used for restraining interference from the primary power source and meanwhile for preventing the primary power source from being polluted by interference generated by the secondary power system. The convertor 7 is the core of the secondary power system, and converts 28V DC power input from the primary power source into a secondary power source required by the airborne equipment, such as various DC power with voltages of 12V, 5V, 3.3 V, 1.5V and the like.
In the above secondary power system, a specific design circuit of the convertor is shown in FIG. 2. The 28V DC power from the primary power source is connected to the convertor via the fuse and the filter. To meet the requirements on resistance to over-voltage surge in Standard GJB191-86, input filter capacitors (such as C1 and C2), a power control chip (such as TPS5450) and other elements in the convertor all need to have a withstand voltage over 80V; however, relatively high withstand voltage brings difficulty in selecting elements, and also results in increased volume of an element and increased cost.